Adjusting for nonadherence or stopping treatments in randomized clinical trials

Randomized clinical trials allocate individuals to different treatments, or, more generally, to interventions and comparators, to determine whether one is better than another. However, after having been randomized to a given intervention, some study participants may not adhere to the assigned protocol. Treatment nonadherence may result from study participants crossing over to the other randomized treatments, taking nontrial medications, or not adhering to the study protocol. All of these situations introduce postrandomization problems that may have to be accounted for in the analysis of data from the trial.